This invention concerns formulations capable of supplying an effective dose of a drug to an animal over a prolonged period of time, and a method of preventing and treating diseases.
The concept of administering a drug to an animal in a form which is capable of supplying an effective dose of the drug to the animal over a prolonged period of time is known in the art. Yolles, for example, in U.S. Pat. No. 3,887,699, describes a formulation comprised of drug intimately dispersed throughout a biodegradable polymeric material which is in the form of a solid film which is implanted subcutaneously into the animal. Schmitt et al., in U.S. Pat. Nos. 3,736,646 and 3,875,937, describe polymers and copolymers which are useful as surgical devices and delivery systems. Boswell et al., in U.S. Pat. No. 3,773,919, disclose formulations which include a lactide polymer and which allegedly permit prolonged release of drugs for a controlled period of time.
The use of polymeric formulations for the slow release of drugs in the treatment of various diseases in animals has suffered in a number of respects. The polymers currently available generally are prepared in such a way that removal of the polymerization catalyst from the polymer is impossible or impracticable. As a result, when the polymer is placed in an animal and degrades over a period of time, undesirable quantities of polymerization catalysts such as metal oxides or strong acids remain in the animal tissues. This is particularly undesirable when the animals so treated are used for meat or other food production. Additionally, most of the polymers known in the art have physical characteristics which necessitate their administration by implantation; see Yolles, U.S. Pat. No. 3,887,699. Such implantation requires the services of one skilled in surgical methods. Moreover, as pointed out by Siegrist et al., in U.S. Pat. No. 3,535,419, the slow release polymeric formulations currently available lack a sufficiently controlled rate of release to be predictable over a useful period of time. This aspect is particularly critical when the active agent being administered can become lethal at elevated doses, and ineffective at insufficient doses.
An object of this invention is to provide formulations comprising a pharmacological agent which is effective prophylactically or therapeutically in combination with a copolymer capable of uniformly releasing the active agent in effective amounts over a predetermined period of time. A further object is to provide copolymeric formulations capable of complete biodegradation into readily metabolized substances. Another object is to provide formulations which can be administered by injection and which, when biodegraded, leave no undesirable residues in animal tissues. Still another object of the invention is to provide a method for effectively preventing the formation of infectious diseases in animals and treating animals suffering from infectious diseases.